There are two states of a User Equipment (UE) in an existing 4G system: a Radio Resource Control (RRC)_CONNECTED state and a RRC_IDLE state.
The UE can perform the following operations in the RRC_IDLE state.
Public Land Mobile Network (PLMN) selection; Non-Access Stratum (NAS) configured Discontinuous Reception (DRX); System information broadcast; Paging; Mobility of a cell reselection mode; the UE is allocated an identifier unique in a specific tracking area; an Evolved Node B (eNB) does not store a context of the UE: transmission and reception in side-link communication during Device to Device (D2D) communication; notification and monitoring in a side-link discovery during a D2D discovery; etc.
The UE can perform the following operations in the RRC_CONNECTED state.
Adjacent cell measurement; D2D communication; a D2D discovery; the UE transmits and receives data with a network: the UE monitors a control signaling channel of a shared data channel to detect the shared data channel for transmission allocated for the UE; the UE reports channel quality information and makes feedback to the eNB; etc.
At present, the UE can transmit and receive user data with the network only after the UE enters an active state, and a cell switching procedure shall be performed when the UE in the active state enters another cell while moving; and since a lot of signaling has to be exchanged in the cell switching procedure, there will be a significant signaling overhead of the UE in the procedure.
In summary, a drawback in the prior art lies in that if the UE needs to transmit with the network, then a cell switching procedure will be performed before the UE enters another cell, thus resulting in a significant signaling overhead of the UE.